The present invention generally relates to ink printing technology, and more particularly to a specialized bladder system for controlling internal pressure levels in an ink containment vessel which is resistant to the corrosive effects of ink materials. The bladder has a novel side wall structure which accomplishes this goal and also prevents the undesired passage of gases (e.g. air) and ink materials therethrough. As a result, the overall longevity and operational efficiency of the entire ink delivery system is improved.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing units using thermal inkjet technology basically involve an apparatus which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon) having a plurality of thin-film heating resistors thereon. The substrate and resistors are maintained within a structure that is conventionally characterized as a "printhead". Selective activation of the resistors causes thermal excitation of the ink materials and expulsion thereof from the printhead. Representative thermal inkjet systems are discussed in U.S. Pat. No. 4,500,895 to Buck et al.; No. 4,794,409 to Cowger et al.; No. 4,509,062 to Low et al.; No. 4,929,969 to Morris; No. 4,771,295 to Baker et al.; No. 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
The ink delivery systems described above (and other units using different ink ejection devices as indicated below) typically include an ink storage unit (e.g. a housing, vessel, or tank) having a self-contained supply of ink therein in order to form an ink cartridge. In a standard ink cartridge, the ink containment unit is directly attached to the operating components of the cartridge to produce an integral and unitary structure wherein the ink supply is considered to be "on-board". However, in other cases, the ink storage unit will be provided at a remote location within the printing system, with the ink storage unit being operatively connected to and in fluid communication with the printhead using one or more tubular ink transfer conduits. These particular systems are conventionally known as "off-axis" printers. Representative off-axis printing systems are illustrated and described in, for example, co-owned pending U.S. patent application No. 08/869,446 (filed on Jun. 5, 1997) entitled "AN INK CONTAINMENT SYSTEM INCLUDING A PLURAL-WALLED BAG FORMED OF INNER AND OUTER FILM LAYERS" (Olsen et al.) and co-owned U.S. Pat. No. 5,975,686 which are both incorporated herein by reference. The present invention shall be applicable to both of these designs (regardless of where the ink storage or containment vessel is located), and may likewise be used in connection with printing devices that employ non-thermal-inkjet technology. Accordingly, while the claimed invention shall be described herein with primary reference to thermal inkjet printing systems, it is also applicable to any ink delivery apparatus which employs a housing or vessel containing a supply of ink therein that is ultimately delivered using at least one ink ejector.
An important consideration in the development of a printing system is the maintenance of proper fluid pressure levels within the ink containment vessel(s) of the system. This factor is particularly important in off-axis systems which normally have fairly large ink supplies associated therewith. While the present invention shall again be applicable to both off-axis and self-contained cartridge-type units as previously noted, it shall be discussed herein with primary reference to off-axis systems and the components associated therewith which will be described in greater detail below. In order to reduce printing system costs and to likewise facilitate a reduction in the operating expense per printed page, off-axis printing systems were developed as previously noted. Off-axis printers basically involve one or more small moving printheads having at least one ink ejector therein (described above) which are connected to relatively large stationary ink storage reservoirs using at least one tubular conduit. In these particular systems, the mass (e.g. weight) of the printhead is significantly reduced so that the overall cost of the printhead drive system and printer size can be minimized. Furthermore, in most cases, this type of system is more economical to operate compared with conventional self-contained ink cartridge units since the ink storage reservoir in an off-axis system can be replaced without requiring replacement of the entire printhead assembly. Accordingly, off-axis printing systems (regardless of the particular ink ejectors being employed) provide many important benefits.
However, typical off-axis printers also include numerous "ink flow restrictions" between the ink storage reservoir and the printhead. These ink flow restrictions (which basically involve barriers to the continuous flow of ink through the system) include but are not limited to (1) multiple internal orifices through which the ink must flow during delivery to the printhead; (2) narrow ink delivery conduits; and (3) shut-off valves. To overcome ink transfer problems caused by these restrictions, the ink compositions originally retained within the ink storage reservoir are transported to the printhead at elevated pressure levels (discussed below). Likewise, to avoid excessive pressure levels which result from this type of system, a pressure reducer/controller is used in order to deliver ink to the printhead at an optimum "back pressure". The term "back pressure" as used herein is generally defined to involve the fluid pressure inside the ink containment vessel during operation.
With continued reference to off-axis printing systems (as well as cartridge-type units with "on-board" ink supplies), it is important that the ink back pressure at the printhead be maintained at a consistent level. Changes in back pressure can adversely affect print density and image quality. Specifically, major changes in back pressure can cause numerous problems including the uncontrolled "drooling" or leakage of ink from the printhead nozzles, depriming of the printing system, and the like. It is therefore highly desirable to create an internal environment within the printing system where the back pressure levels are maintained at a stable, consistent, and minimal level.
There are several causes for undesired changes in system back pressure. One cause of primary importance involves the trapping of air within the printing system (particularly the ink containment vessel or other storage chamber operatively connected to the printhead), followed by changes in environmental parameters including altitude and temperature. As used throughout this discussion, the term "air" shall be broadly defined to encompass not only air from internal and external sources, but volatile compositions which outgas from the ink materials being delivered, as well as other gases which are ambiently present in the printing system. Representative and non-limiting volatile compositions used in connection with ink formulations as "vehicles", "solvents", "humectants", and the like include but are not limited to water and organic materials such as 2-pyrrolidone, 1,5-pentanediol, N-methyl pyrrolidone, 2-propanol, ethoxylated glycerol, 2-ethyl-2-hydroxymethyl-1,3-propanediol, cyclohexanol, and others known in the art for this purpose. Air (and/or other gaseous materials as defined above) entrapped within an ink delivery system will interact in accordance with the "Ideal Gas Law" [PV=nRT] wherein changes in any one of the parameters associated with this formula (e.g. temperature, volume, etc.) will cause corresponding changes in printhead back pressure. These changes are undesirable for the reasons given above. Finally, an additional problem which causes changes in system back pressure involves a delay which typically occurs between the time the printhead begins ejecting ink to the point at which operation of the selected pressure regulator is initiated.
Regarding a preferred sub-system for controlling back pressure levels in an ink delivery apparatus, the present invention primarily (but not exclusively) involves the use of a specialized arrangement of components which will now be discussed. The pressure control system of primary interest in this case is summarized in co-owned U.S. Pat. No. 5,975,686 which is referenced above, incorporated herein by reference, and relied upon for priority in this case. More detailed information regarding this particular pressure control system will be presented below in the Detailed Description of Preferred Embodiments section. Basically, this type of system employs multiple components which cooperate to precisely regulate back pressure levels within the ink containment vessel in the printer unit of interest. Subject to a more in-depth discussion provided below, this back pressure control system involves the use of an external ink supply stored within a "reservoir" which is in fluid communication with a chamber (also known as an "accumulator" or "ink containment vessel"). Fluid communication occurs via one or more tubular ink flow conduits. The term "tubular" as used herein shall encompass a structure having a central passageway therethrough that is surrounded by a continuous side wall. It should be noted that the term "ink containment vessel" as used herein shall involve any vessel (or vessels) which are designed to contain ink that is ultimately delivered to the printhead. In the example provided above (and discussed in U.S. Pat. No. 5,975,686 the ink containment vessel primarily involves the "accumulator" structure directly associated with the printhead as indicated below. However, this term may also be construed to cover the ink reservoir unit in the system if pressure control is needed therein. It should therefore be understood that the claimed invention shall not be limited to any particular location or type of ink containment vessel which can encompass any housing, tank, or equivalent structure designed to retain ink therein for subsequent transfer to a printhead.
In the system of U.S. Pat. No. 5,975,686 the ink containment vessel is, in turn, operatively connected to and in fluid communication with a printhead containing one or more ink ejectors. In a non-limiting and preferred embodiment, the ink ejectors will consist of thin-film resistors. The term "operatively connected" as previously noted shall involve a system in which the printhead is directly connected to the ink containment vessel or in fluid communication therewith using one or more intermediate transfer structures including but not limited to single or multiple tubular conduits.
Positioned within the ink containment vessel (which, in this non-limiting embodiment, functions as an "accumulator" as previously noted) is a back pressure regulator. The term "back pressure" is defined above. The regulator maintains the fluid back pressure in the ink containment vessel/printhead at a substantially constant value so that ink is supplied to the printhead in a complete and uniform manner. This goal is accomplished using a very special component that is again described in U.S. Pat. No. 5,975,686. Basically, a plurality of spring-biased lever members (in the form of "arm-like" structures) are provided within the ink containment vessel that resiliently engage an inflatable (and deflatable) bag member characterized herein as a flexible "bladder". The interior region of the bladder (e.g. the inside of this component) is in fluid communication with ambient air through a series of valves and other related components. The term "bladder" shall encompass a wide variety of different devices including but not limited to any flexible inflatable/deflatable structure regardless of shape, form, or material which is designed to receive one or more fluids (optimally gases) therein.
As back pressure conditions inside the ink containment vessel change, the bladder is designed to inflate and deflate as discussed in greater detail below. Inflation and deflation of the bladder will activate various valves and/or change the volumetric characteristics of the ink containment vessel. This process will accurately control back pressure levels within the ink containment vessel and accompanying printhead. However, to ensure maximum effectiveness, it is important that the bladder have a high degree of structural integrity, longevity, and resistance to chemical deterioration (e.g. "corrosion") by ink materials. Corrosive ink ingredients are discussed above and typically involve organic solvents, acidic dyes, and the like. The bladder should likewise have a side wall which is able to prevent the leakage of air (also defined above) and ink materials into the bladder. The leakage of these compositions into the bladder could cause undesired pressure imbalances and a loss of effectiveness.
Prior to development of the present invention, a substantial need existed for a flexible pressure control bladder designed for use in an ink containment vessel which is resistant to ink corrosion problems, prevents air passage through the bladder side wall, and is characterized by improved longevity. The claimed invention satisfies these needs in a unique and effective manner. Specifically, a novel pressure control bladder, an ink delivery system using the bladder, and a method for producing an efficient ink delivery system are disclosed which provide many benefits. These benefits include (1) the avoidance of ink-based bladder deterioration problems; and (2) the prevention of air, ink, and other materials from passing through the bladder side wall. As a result, high levels of operating efficiency, print quality, pressure control, and longevity are maintained in connection with the ink delivery system under consideration. These and other benefits associated with the claimed invention (as well as the specific features thereof) shall be discussed in considerable detail below.
As a further preliminary note, it shall be understood that the construction materials and bladder designs provided in the Detailed Description of Preferred Embodiments section are not restricted to any particular ink delivery system including the one shown in co-owned U.S. Pat. No. 5,975,686. Instead, the materials, components, methods, and techniques claimed in this case are applicable to any ink delivery system in which a flexible bladder is employed within a chamber containing ink materials in order to achieve proper ink delivery and effective pressure control, with the invention also being applicable to ink storage bladder units in which a supply of ink is retained directly therein.